- Grade beam - while not seen in typical slab-on-grade diagrams - it is the thickened part of a slab-on-grade - 
- Slab is easier and cheaper to build than a pier and beam foundation. 
- Grade Beam - 
- Grade beam is the thickened outer edge of the slab foundation. 
- Spread footing - 'inverted T' actually holds the pressure on the soil. Grade beam functions like a beam - spanning 2 deep piles, not relying on soil underneath for support. 
- Grade beams connect column foundations together - 
- Slab foundations are used on flat lots . Supported directly be ground.
- Shallow and deep are 2 general classes. Deep ones go down to bedrock. 
- Grade beam is min 8" wide, and depth is the length of span it supports 
- Compared to typical foundation, uses less concrete.